1. Field of the Invention
The invention relates to a needle selection mechanism in knitting machines. This mechanism is particularly appropriate for high speed machines having electronic programming and may also be applied with very slim, narrow pitch needles and in high speed machines, as is the case of hosiery machines.
For simplicity, reference is made in the following description to the application to circular machines, this representing no limitation however to the application in flat bed machines, this latter application also being of particular interest.
2. Description of the Related Art
Circular knitting machines have a rotating cylinder provided with axial grooves along which there slide the needles which engage, either with their own butt or through pushers provided with butts, fixed cams (camboxes) which determine the vertical stroke of each needle.
The development of a knitting programme requires that the needles passing over each cambox may be raised and held at preset heights or not raised.
This operation is known as selection and is effected in modern machines with fixed electromagnets which act directly or indirectly on the butts of the needle pushers.
The modern, higher speed machines are provided with rocking pushers, provided in turn with butts for axial raising and a plurality of programmable radial butts which, when pushed by the selection cams, determine the travel of the needle to the desired height.
The selection speed, which may be defined as the number of needles which may be selected per second, is substantially restricted by the angular development of the cam profiles, by the response times of the electromagnets and by the large masses to be accelerated, all the larger the greater the degree of selection which it is wanted to attain.
It is sufficient to say that, to attain total programmability of the needles, there must be pushers provided with as many butts as there are needles, multiplied by the number of levels to be attained. Therefore, in practice, the programming of the needles imposes limits and above all requires the replacement of the pushers for different types of fabric to be knit and, therefore, production downtimes and cost of new components.